BERLIN (Reuters) - German Chancellor Angela Merkel's conservative Christian Democrats fell to third place in a state election on Sunday behind the center-left Social Democrats (SPD) and anti-immigrant Alternative for Germany (AfD) party, TV exit polls showed.

In a stinging defeat for Merkel one year ahead of parliamentary elections, the upstart AfD won 21 percent of the vote in their first election in Mecklenburg-Vorpommern state by campaigning hard against the chancellor's policies on refugees, according to an exit poll by the ARD TV network.

The SPD, which has ruled the rural state on the Baltic coast with the CDU as junior coalition partners since 2006, won 30.5 percent of the vote, down from 35.6 percent in the last election in 2011. The CDU won 19 percent, down from 23 percent in 2011, and its worst result ever in the state, the broadcaster said.

The far-left Left Party won 12.5 percent, down from 18.4 percent five years ago, while the pro-environment Greens won 5 percent, down from 8.7 percent. The far-right NPD was knocked out of the state assembly, falling below the 5 percent threshold for the first time since 2006 with 3.5 percent, down from 6 percent in 2011.